Statistical comparison as a test of hypotheses about the coincidence of distribution parameters is considered. This allows defining whether the discrepancy in estimations of the distribution parameters of safety indicators is significant or can be justified by inessential changes in the conditions of the experiment-random drifts. Each adverse event is assigned a weight that reflects the probability that it can result in an adverse outcome in a particular flight. Risk (hazard) assessment is represented as a product of the mean value of weight n0 of adverse event Kn and frequency of occurrence Fn of events during the period of time analysed.